Performance of beef cows of different genetic groups in natural and cultivated pastures

Ricardo Zambarda Vaz,José Neuman Miranda Neuman,Patrícia Alessandra Meneguzzi Metz Donicht,Dari Celestino Alves Filho,Fabiano Nunes Vaz,Leonir Luiz Pascoal,João Restle,Paulo Santana Pacheco

doi:10.14393/bj-v32n1a2016-26504

Abstract

The objective was to assess the performance of 96 pregnant cows of the genetic groups (GG) Charolais (C), Nellore (N), ½ CN and ½ NC, subjected to the following treatments: kept exclusively in natural pastures (NP) throughout the experimental period; kept in cultivated pastures (CP) from July 15 to Setp 15 (CPNP) or from Sept 15 to Nov 15 (NPCP) and the remainder of the experimental period in NP. The weight at the end of the first grazing period (Sept 15) was higher for the CPNP cows than those of the NPCP and NP. The weight at the end of the second period (Nov 15) was 456, 428 and 392 kg respectively for NPCP, CPNP and NP. At calving, the heaviest cows were the CPNP, followed by the NPCP and the NP. At weaning, 90 days postpartum, the heaviest were the NPCP, followed by the CPNP and NP. Nelore cows were less heavy in all evaluations, followed by C, with the F1s’ weight higher than the purebreds. The grazing sequences did not affect the percentages of the cows in estrus and pregnancy, but did influence the invervals between calving and first estrus postpartum (ICE). The GG influenced the rate of cows in estrus, pregnant and the ICE which was lower in the F1 (103 days), followed by the C (109 days) and had the largest interval N (119 days). The grazing sequences affect the average daily weight gain (ADG) of calves until weaning at 90 days of age. The GG of the calf affected the ADG at to 210 days.

Highlights

The low birth rates in addition to adversely affecting the offtake and productivity indicators of the herds (BERETTA et al, 2002), reduce the possibility of genetic improvement through selection due to low availability of replacement females (VAZ; LOBATO, 2010)
The animals are born with their sexual behavior linked to factors related to the genetic load itself, but these factors interact with the environment promoting or inhibiting their reproductive behavior (VAZ et al, 2012). Their reproductive performance is related to the management, health care and nutritional level to which they are subjected. This fact is accentuated in the southern part of Brazil where most of the cattle farms are built on natural pastures, the main source of feed for the livestock, where low production and quality limit the genetic potential response of the animals (RESTLE et al, 2005)
With the nutritional deficit imposed on livestock rearing by overloading the animals per hectare (FAGUNDES et al, 2003), the cows arrive at calving with a low average body condition, and with lactation the body condition score decreases even more, not having the minimum conditions to return to reproductive activity in the subsequent breeding season

Summary

Introduction

The low birth rates in addition to adversely affecting the offtake and productivity indicators of the herds (BERETTA et al, 2002), reduce the possibility of genetic improvement through selection due to low availability of replacement females (VAZ; LOBATO, 2010). The animals are born with their sexual behavior linked to factors related to the genetic load itself, but these factors interact with the environment promoting or inhibiting their reproductive behavior (VAZ et al, 2012). Their reproductive performance is related to the management, health care and nutritional level to which they are subjected. This fact is accentuated in the southern part of Brazil where most of the cattle farms are built on natural pastures, the main source of feed for the livestock, where low production and quality limit the genetic potential response of the animals (RESTLE et al, 2005). Studies show the benefits of using crossbreeding to reduce the age of puberty as well as for the subsequent reproductive performance in beef cows (RESTLE et al, 2003)

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